Control device for lifts



June 5, 1934.

E. B. THOMPSON 1,961,465

CONTROL DEVICE FOR LIFTS- Filed Oct. 21, 1933 2 Sheets-Sheet l f'zuenfor CONTROL DEVICE FOR LIFTS Filed Oct. 21,1933 2 Sheets-Sheet 2 Patented cute 5, 1934 PATENT OFFICE I 1,961,465 CONTROL DEVICE FoR LIFTS Elmer B. Thompson, Des Moines, Iowa, assign'or to Swanson & Thompson, Des Moines, Iowa, a partnership composed of F. W. Swanson and Elmer B. Thompson Application October 21,

4 Claims.

My invention relates to the art of automobile lifts of the class which is operated by compressed air. With lifts of this class now in common use, it is customary to use compressed air from the same air storage tank that supplies compressed air for the lift for other purposes, such for instance as tire filling, grease gun operation, etc. It is also customary with said lifts to lower the lift by discharging to the atmosphere the compressed air used in raising the lift, and with said lifts it frequently happens that the compressed air stored in the tank is so reduced in amount that relatively long delays are occasioned before a lift may be raised, and furthermorepn account of such low air pressure, the lift may move downwardly and cause accidents and damages. I

The objects of my invention are to provide, in a lift of this character, means whereby the air compressor is automatically operated during the lowering movement of the lift to withdraw air from the lift cylinder and force it into the air storage tank, thereby avoiding waste ofpower as applied to the air compressor, governing the rate of descent of the lift to safe limits, and constantly maintaining in the air storage tank a sufficient pressure to quickly raise the lift immediately after it has been lowered.

A further object is to provide in a lift of this character a single air control device including a lever normally held in a neutral position for preventing any flow of air forraisingor lowering the lift, and so constructed-that when moved to one position, it will permit the passage of air from the air storage tank to the lift cylinder for raising the lift, and in another position permit the passage of air from the lift cylinder back to the air compressor and air storage tank, and when in said latter position it will automatically close an electric circuit for operating the motor of the air compressor, thereby eliminating all possibility of having the lift move downwardly on account of reduced air pressure in the air storage tank, and also making it impossible to lower the lift without at the same time conducting the compressed air in the lift cylinder into the 'air storage tank, and thereby assuring an immediately available supply of compressed air in the air storage tank for lift raising or other purposes,

My-invention consists in the construction, arrangement and combination of the various parts are attained, as hereinafter more fully set forth,

1933, Serial No. 694,563 (01. 138-9) pointed out in my claims, and illustrated in the accompanying drawings, in which:

Figure 1 shows a side elevation of an appara tus embodying my invention, partly in section.

Figure 2 shows a detail side elevation of same with the lift omitted, and with the manually controlled valve and switch mechanism shown in section, and also with the pressure controlled electric switch shown in section.

Referring to the accompanying drawings, I have'used the reference numeral 10 to indicate a storage tank for compressed air. Mounted upon the storage tank is an air compressor 11 of ordinary construction, operatively connected with an electric motor 12. An air conducting pipe 13 leads from the compressor to the tank, and has a one-way check valve 14 of ordinary construction mounted therein for limiting the movement of the air in one direction only away from the compressor. In Figure 2 the open position of the valve is indicated by dotted lines at 15.

Leading to the compressor 11 is an air conducting pipe 16 having one end open to the atmosphere at 17. In Figure 2 the arrow 18 indicates the direction of flow through the open end 17, and this pipe is provided with a oneway check valve 19. In Figure 2 the open position of this valve is indicated by dotted lines 20.

For automatically controlling the electric m0- tor 11 and for maintaining a predetermined air pressure within the tank 10 I have provided a pressure controlled electric switch indicated generally by the reference numeral 21, and communicating with the tank 10 through a pipe 22. This pressure switch is provided with the usual flexible diaphragm 23 connected with a pivoted switch lever 24 carrying a circuit closer 25 which when in its closed position, completes a circuit through the contacts 26. These pressure controlled switches are in common use and hence detail description thereof is unnecessary. This switch device is included in an electric circuit 27 in which the motor 12 is also included, so that when the switch is closed the motor is operated.

My device is intended for use with an ordinary automobile lift or the like, and as shown -in Figure 1 the liftcomprises a cylinder 28 with a verticallymovable piston 29 therein, and a lift platform 30 at the top of the piston, and communicating with the bottom of the cylinder is a pipe 31 toconduct air to and from the cylinder.

. For controlling the passage of air to and from the lift cylinder, I have provided a combined manually operated air control and electric switch device. This comprises a valve casing indicated generally by the numeral 32 and communicating at one end with the pipe 13 and at its other end with the pipe 16, and at a midway point with the pipe 31.

A valve 33 controls the flow of air from the pipe 13 to the interior of the valve casing 32, and another valve 34 controls the passage of air from the interior of the valve casing 32 to a pipe 16 leading to the compressor. The valve 33 is normally held in closed position by a spring 35, and the valve 34 is also held in closed position by a spring 36.

Pivotally mounted between the valves 33 and 34 is manually controlled lever 37 having arms 38 projected over the valves 33 and 34 with an arm 39 projected downwardly into a casing 40, and this arm 39 is provided with an electric switch element 41 to co-operate with the contact points 42 for forming an electric switch.

These parts are so arranged, as clearly illustrated in Figure 2, that when the lever 37 is in an upright position the arms 33 will be above the valves 33 and 34, so that both valves will stand closed and all flow of air from the tank or cylinder will be stopped. When, however, the lever 3'7 is moved to the position shown in Figure 2, the valve 34 will be opened and the electric switch 41 will be closed. This switch is connected to conductor wires 43 which are included in the electric circuit 27, and so arranged that when the switch is closed, the circuit will be completed through the electric motor 12 and the motor operated for operating the compressor, and this means for operating the motor is entirely independent of the automatic pressure switch included in the same circuit.

In the said position of the lever 37, the valve 34 will be opened and the motor 12 operated, and hence air will be drawn into the compressor through the pipe 16' and the valve chamber 32, and the pipe 31 from the cylinder, and at the same time air will be forced from the compressor through the pipe 13 to the compressed air tank 10. This operation will continue as long as the operator keeps his hand upon the lever 37 and holds it in said position, and the operator usually does this until the lift is in its fully lowered position. If, however, the operator should at any time during movement of the lift release the lever 37, it will be instantly moved by the springs 35 and 36 to normal position, where the flow of air from the cylinder will be stopped and the switch device 41 and 42 will be opened.

When the lever 37 is moved to its opposite limit of movement from that shown in Figure 2, then the valve 34 will remain closed and the valve 33 will be opened, and the switch 41 and 42 will be opened, so that air will flow from the compressed air cylinder through the pipe 13, the valve casing 32 and the pipe 31 to the lift cylinder. Mounted upon the pipe 13 is an ordinary air pressure gauge 44 of ordinary construction.

In practical use with my improved lift control device, when used in connection with an automo bile lift, I preferably so adjust the automatic pressure controlled electric switch" so that it will automatically close the circuit and operate the motor until the pressure within the tank 10 reaches about 125 pounds, when the flexible diaphragm is elevated and the switch opened, and I preferably employ a pressure control switch device of this character in which the electric switch will automatically close when the pressure within the tank 10 falls to about 120 pounds.

When it is desired to raise the lift, the operator grasps the lever 37 and moves it to the right as shown in Figure 1, for opening the valve 33, and when this is done compressed air in the tank will flow to the bottom of the cylinder 28 and raise the piston 29.

It is highly important in a lift device of this character that sufficient air pressure be maintained to hold the lift in its elevated position as long as desired, and it should be explained also that where these lifts are used, it is customary to use the compressed air for other purposes such for instance as tire filling, compressed air grease gun serviceand the like, so that it sometimes happens that when the lift is elevated, the air pressure within the tank 10 falls below the amount required for maintaining the lift in its elevated position.

However, the pressure controlled electric switch will operate the motor and compressor Whenever the pressure in the tank falls below a predetermined limit, so that there is always a sufficient supply of compressed air in the tank to maintain the lift in its elevated position. Lifts of this kind are commonly provided with these air pressure electric switches for controlling the motor.

In lifts of this kind now in common use, and when it is desired to lower the lift, the manually controlled valve is opened to permit the discharge of air from the cylinder 28 to the atmosphere, and if the lift is raised and shortly thereafter again lowered, the amountof compressed air thus released to the atmosphere so reduces the pressure within the tank 10 that it requires a considerable length of time to again restore this pressure to normal and during that time the compressor is being operated at full capacity and generates an objectionable amount of heat due to its relatively long continued operation.

With my improvement, however, the lowering of the lift is accomplished by pumping the air from the cylinder 28 through the compressor back to the tank 10, and I have demonstrated that in actual practice the lowering of the lift may be accomplished at about the speed desired, and since the air in the cylinder and the tank is compressed to about the same extent, the removal of the air from the cylinder is accomplishedquickly and with no objectionable heating of the air compressor.

I have found with my device in actual use, and when the lift is elevated and held elevated for a short period of time, the pressure in the tank 10 will soon be restored to normal, and then when the lift is lowered, the pressure in the tank 10 will be raised to some extent above normal, but this, however, is not objectionable. This pressure in actual practice amounts to about 150 pounds, and then air may be used either for again elevating the lift, or for other purposes, and the motor will remain inoperative until the pressure in the tank 10 has again been reduced to normal, and with my device I find in practice that the lift may be again raised promptly after it has been lowered and without the necessity of waiting until the tank pressure is again rebuilt to normal.

My improved apparatus provides a safety fea ture which is highly desirable in that the only means forlowering the lift is by pumping the air through the compressor to the tank. Hence the lift is lowered at a uniform speed and cannot drop quickly, regardless 'of the amount of pressure within the tank 10, and the lift will "automatically stop and stay in any position of elevation instantly upon the release of the lever 37.-

When the lift is in use and in an elevated position with an automobile or other weight thereon, the weight of the lift and the automobile maintains a pressure upon the air in the cylinder, which pressure is uniform during the entire lowering stroke of the piston, hence because it is thus reduced in volume it is rapidly drawn out by the compressor.

I claim as my invention:

1. In a lift device, the combination of an air storage tank, an air compressor arranged to deliver compressed air to said tank, an electric circuit having therein an electric motor for operating said compressor, and an electric pressure control switch for automatically starting and stopping said motor and said compressor in accordance with the pressure in said tank to thereby maintain an approximately uniform pressure on said air storage tank, a lift cylinder, a lift piston in said cylinder, means for exerting downward pressure upon the said piston, means for conducting air from said tank to said cylinder and back to said compressor, an air controlling device in said means for conducting air and designed in one position to permit the flow of air from said cylinder to said compressor, and in another position to permit the flow of air from said tank to said lift cylinder, an electric. switch operatively connected with said air control device and included in the circuit of said electric-motor and arranged to short circuit said automatic electric pressure control switch rendering it inoperative and to close said electric circuit and operate said motor when said air control device is in position for permitting the passage of air from said cylinder to said compressor.

2. In a lift device, the combination of a cylinder, a piston in the cylinder, an air compressor, an air storage tank in communication with the compressor, means for conducting air from the storage tank to the cylinder, means for conducting air from the cylinder to the compressor, manually controlled valve mechanism for permitting the passage of air either from said tank to said cylinder or from said cylinder to said compressor, an electric motor for driving said compressor, an electric circuit in which said motor is included, a pressure controlled electric switch device included in said circuit and automatically operated by the pressure within said storage tank for starting and stopping said motor in accordance with the pressure within the storage tank to thereby maintain an approximately uniform pressure within said storage tank, an electric switch device included in said circuit and operatively connected with said manually controlled. valve mechanism and arranged to operate said motor when said valve mechanism is in position for permitting the flow of air from said cylinder to said compressor and at the same time render ineffective that part of the circuit in which said pressure switch is included, whereby when said valve switch is closed said pressure switch is inoperative, and when said valve switch is open said pressure switch is free to be operated by the pressure within said storage tank.

3. In a lift device, the combination of a cylinder, a piston in the cylinder, an air compressor, an air storage tank in communication with the compressor, means for conducting air from the storage tank to the cylinder, means for conducting air from the cylinder to the compressor, manually controlled valve mechanism for permitting the passage of air either from said tank to said cylinder or from said cylinder to said compressor, an electric motor for driving said compressor, an electric circuit in which said motor is included, a pressure controlled electric Switch device included in said circuit and automatically operated .by the pressure within said storage tank for starting and stopping said motor in accordance with the pressure within the storage tank to thereby maintain an approximately uniform pressure within said storage tank, an electric switch device included in said circuit, and means operated upon the opening of said valve mechanism to position for permitting the flow of air from the cylinder to the compressor for closing said switch to start said motor and at the same time render ineffective that part of the circuit in which said pressure switch is included, whereby when said valve switch is closed said pressure switch is inoperative, and when said valve switch is open said pressure switch is free to be operated by the pressure within said storage tank.

4. In a lift device, the combination of an air storage tank, an air compressor arranged to deliver compressed air to said tank, an electric circuit having therein an electric motor for operating said compressor, and an electric pressure control switch for automatically starting and stopping said motor and said compressor in accordance with the pressure in said tank to thereby maintain an approximately uniform pressure on said air storage tank, a lift cylinder, a lift piston in said cylinder, means for exerting downward pressure upon said piston, means for conducting air from said tank to said cylinder and back to said compressor, an air controlling device in said means for conducting air and designed in one position to permit the flow of air from said cylinder to said compressor, in another position to permit the flow of air from said tank to said lift cylinder, and in a normal position to prevent flow of air to or from said cylinder, an electric switch operatively connected with said air control device and included in the circuit of said electric motor and arranged to short circuit said automatic electric pressure control switch to render it ineffective and to close said electric circuit and operate said motor when said'air control device is in-position for permitting the passage of air from said cylinder to" said compressor, and means for automatically returning the air controlling device to its normal position and for opening the short circuiting switch.

ELMER B. THOMPSON. 

